The term **78-2-R** typically refers to a specific type of **Single-Turn Trimpot (Trimmer Resistor)** produced by manufacturers like **Bourns** (specifically the 3386 or 3362 series variations) or other electronic component suppliers. Below is a breakdown of the technical specifications, characteristics, and usage of this part. --- ### 1. General Specifications The "78-2-R" designation usually follows a manufacturer-specific coding system for potentiometers. Here are the common technical parameters associated with this class of components: | Feature | Description | | :--- | :--- | | **Component Type** | Cermet Trimmer / Variable Resistor | | **Adjustment Type** | Top Adjust or Side Adjust (model dependent) | | **Terminal Style** | Through-hole (PC Pin) | | **Power Rating** | Typically 0.5 Watts at 70°C | | **Resistance Range** | Often denotes 2.0 Ohms (if "2-R" is the value) or a series code | | **Tolerance** | ±10% or ±20% | | **Temperature Coeff.** | ±100 ppm/°C | --- ### 2. Internal Construction These electronic parts are made using **Cermet** (Ceramic-Metal) technology. * **Resistive Element:** A thick film of cermet is deposited on a ceramic substrate. * **Wiper:** A metal contact moves along the track to vary the resistance. * **Housing:** Usually made of fire-retardant plastic, sealed to withstand wave soldering and board washing. --- ### 3. Pinout Configuration Trimmer resistors of this series typically have three pins: 1. **Pin 1:** Fixed End (Start of resistive track) 2. **Pin 2:** Wiper (The moving contact that provides the variable output) 3. **Pin 3:** Fixed End (End of resistive track) --- ### 4. Common Applications These parts are used for "set and forget" adjustments on a Printed Circuit Board (PCB). * **Voltage Calibration:** Adjusting the output voltage of a power supply module. * **Sensor Tuning:** Calibrating the threshold of an infrared or moisture sensor. * **LCD Contrast:** Controlling the brightness or contrast of character displays. * **Timing Circuits:** Fine-tuning the RC time constant in 555 timer circuits. --- ### 5. Identification Tips If the "78-2-R" is part of a larger part number (like **Bourns 3386P-1-103**), the suffix codes often mean: * **78/33xx:** The physical size and series. * **-1 / -2:** The terminal style (pin layout). * **R:** Often indicates compliance with **RoHS** (Restriction of Hazardous Substances) standards. ---